Question

Which from following pair of elements have one electron in 5d-subshell in observed electronic configuration?

• A. Sm (Z=61) and Eu (Z=63)
• B. Gd (Z=64) and Lu (Z=71)
• C. Ce (Z=58) and Nd (Z=60)
• D. Lu (Z=57) and Dy (Z=66)

Answer 1

Answer: (B)

Gd (Z=64) and Lu (Z=71)

Answer 2

we need to examine the electron configurations of the elements.
(A) Sm (Z=61) has the electronic configuration: [Xe] 4f6 6s2 Eu (Z=63) has the electronic configuration: [Xe] 4f7 6s2
In both cases, the 5d-subshell is not yet occupied, so this pair does not fulfill the given condition.
(B) Gd (Z=64) has the electronic configuration: [Xe] 4f7 5d1 6s2 Lu (Z=71) has the electronic configuration: [Xe] 4f14 5d1 6s2
In this pair, both Gd and Lu have one electron in the 5d-subshell, satisfying the condition.
(C) Ce (Z=58) has the electronic configuration: [Xe] 4f1 5d1 6s2 Nd (Z=60) has the electronic configuration: [Xe] 4f4 5d0 6s2
In this pair, only Ce has one electron in the 5d-subshell, so it satisfies the condition.
(D) Lu (Z=57) has the electronic configuration: [Xe] 4f14 5d1 6s2 Dy (Z=66) has the electronic configuration: [Xe] 4f10 5d0 6s2
In this pair, only Lu has one electron in the 5d-subshell, so it satisfies the condition.
Therefore, the correct pair of elements is: (B) Gd (Z=64) and Lu (Z=71)